1. Field of the Invention
The present invention relates to a proportional solenoid valve that displaces a valve element by applying a current to a solenoid coil and obtains an output pressure proportional to the value of the applied current, and a control method for the proportional solenoid valve.
2. Description of the Related Art
In a conventional proportional solenoid valve, when a high current exceeding an ordinary working current range is applied to a solenoid coil or when a high pressure is temporarily exerted on a valve element due to pulsation of an input pressure, for instance, a plunger is displaced to exceed an ordinary operating range. In this case, if an end surface of the plunger is attracted so as to directly contact an end surface of a core, there occurs a malfunction of the plunger and output pressure becomes unstable. In view of this problem, a stopper made of a non-magnetic material is arranged between the end surface of the plunger and the end surface of the core (see Japanese Utility Model Application Laid-Open No. 61-63088, for instance).
In the conventional proportional solenoid valve described above, however, the stopper is arranged between the plunger and the core, so that the number of components and the number of assembly steps are increased, which leads to an increase in cost. In addition, there is a problem that variations occur in magnetic attraction force characteristics.